Sayyiduna Zayd bin Thabit (may Allah be pleased with him) said: I recited Surah al-Najm before the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) did not prostrate.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3753
(a) It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) prostrated in Surah al-Najm, and all the people prostrated with him (peace and blessings be upon him) except two men. Those two wanted to make themselves conspicuous (by not prostrating).
(b) Imam al-Shafi'i (may Allah have mercy on him) said: Those two men would not have abandoned an obligation; and had they abandoned it, the Messenger of Allah (peace and blessings be upon him) would certainly have ordered them to repeat it.
As for the hadith of Zayd bin Thabit (may Allah be pleased with him), Zayd (may Allah be pleased with him) was the one reciting. When the reciter did not prostrate, the Messenger of Allah (peace and blessings be upon him) did not prostrate either; and had it been obligatory, the Messenger of Allah (peace and blessings be upon him) would have ordered him to prostrate as well.
Imam al-Shafi'i (may Allah have mercy on him) argued from the earlier hadith of the Prophet (peace and blessings be upon him) about the obligation of the five prayers, in which a man asked whether any other prayer (besides these five) was obligatory, and he (peace and blessings be upon him) said: "No, unless you do voluntary worship."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3754
Hadith Gradingمحدثین:حسن
Hadith Takhrij«حسن۔ بدون قصه الرجلين، قال ابن ابي حاتم في العلل 468»
It is narrated from Rabi'ah bin Abdullah (may Allah have mercy on him) that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) recited Surah al-Nahl on Friday (on the pulpit). When the verse of prostration, "And to Allah prostrates whatever is in the heavens and whatever is on the earth" [Surah al-Nahl: 49], came, Sayyiduna Umar (may Allah be pleased with him) came down from the pulpit and prostrated, and the people prostrated too. On the following Friday he recited the same surah again, and when he reached the verse of prostration he said: O people, we have not been commanded to prostrate; so whoever prostrates has done well and has done what is right, and whoever does not prostrate, there is no sin upon him. And Sayyiduna Umar (may Allah be pleased with him) did not prostrate. Nafi' (may Allah have mercy on him) added: Your Lord has not made the prostration of recitation obligatory upon us, but has left it to our choice.
(b) This is through the chain of Imam al-Bukhari (may Allah have mercy on him). At its end is this addition: Nafi' (may Allah have mercy on him) narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that Allah has not made the prostrations of recitation obligatory upon us, except that if we wish, we may perform them.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3755
(a) Hisham bin Urwah (may Allah have mercy on him) narrates from his father that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) recited a verse of prostration on the pulpit on Friday, so he came down from the pulpit and prostrated, and the people prostrated with him. Then on the following Friday he recited the same verse of prostration; the people got ready to prostrate, whereupon Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) said: Wait a moment; Allah Almighty has not made these prostrations obligatory upon us, rather they depend on our choice. Sayyiduna Umar (may Allah be pleased with him) recited the verse of prostration but did not prostrate, and he also stopped the people from prostrating.
(b) Imam al-Bukhari (may Allah have mercy on him) said: Someone said to Sayyiduna Imran bin Husayn (may Allah be pleased with him): A man hears a verse of prostration although he had not sat down to listen to it; what should he do? He said: Then what do you think if he had sat down for it? It was as if he did not consider it obligatory upon him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3756
Hadith Gradingمحدثین:ضعيف
Hadith Takhrij«ضعيف۔ للانقطاع بن عروة وعمر، والله اعلم»
In the narration of Sufyan al-Thawri (may Allah have mercy on him), Ibn Sirin (may Allah have mercy on him) said: I asked Sayyidah Aishah (may Allah be pleased with her) about the prostrations of the Qur'an, and she said: "It is a right of Allah which you fulfil, or a voluntary act which you perform voluntarily. There is no Muslim who makes a single prostration to Allah but that Allah Almighty raises him a degree by it, or removes a sin from him by it, or combines both for him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3757
Hadith Gradingمحدثین:ضعيف
Hadith Takhrij«ضعيف۔ ابن سيرين لم يسمع من عائشة ولا حداها»